A typical broadband setup involves a router device with a Digital Subscriber Line (DSL) or cable link to an Internet Service Provider (ISP) connected to wide area networks such as the Internet and resources such as file/video/content servers and other correspondent nodes.
Typically, many mobile devices do not have wired interfaces such as Ethernet to connect to the router using a wired connection. To address this, and to provide flexible connectivity, the IEEE 802.11 family of standards relating to “Wi-Fi” is now a popular system for allowing computing devices to communicate wirelessly using radio wave transmission. Groups of computing devices all communicating via a common wireless access point are known as wireless local area networks (WLANs).
In such systems, when a mobile device is in communication with a correspondent node, application data is sent in IP data packets from a mobile device to the wireless access point via Wi-Fi, from the router to the ISP core network via xDSL and from the ISP core to wide area network protocols to reach the correspondent node.
Mobile/Cellular networks also provide data connectivity although typically over a wide area instead of local area in WLANs. Mobile Network Operators (MNOs) maintain Public Land Mobile Networks (PLMNs) formed of a number of radio base stations known as macrocells connected to a network core which provides control functions as well as connectivity to wide area networks such as the Internet. An example of a cellular network protocol is Long Term Evolution (LTE) sometimes known as 4G.
In order to supplement the coverage of macrocells, shorter range base stations such as picocells and femtocells, collectively known as small cells, are being deployed. In addition to the smaller geographical coverage, the small cells differ from macrocells in that they are connected to the mobile network core, an Evolved Packet Core (EPC) in LTE, using a broadband connection instead of dedicated cabling. This allows LTE small cells to be co-located or even integrated into a wireless access point router device.
In LTE small cells, when a mobile device is in communication with a correspondent node using a small cell instead of Wi-Fi, application data is sent in IP data packets from the mobile device to the small cell in the router via LTE, from the router to the ISP core network via xDSL, from the ISP core to a mobile network core, and from the mobile network core to a, or a number of, wide area networks to reach the correspondent node.
Today there are many mobile devices which combine both Wi-Fi and Cellular (LTE in particular) radios allowing the ability to connect to wide area network resources via both Wi-Fi and cellular protocols. Typically, the mobile devices are configured to only use one of the wireless technologies at any given time to save power. Therefore when both types of wireless network are available, a decision must be made over which connection to use in any given circumstance.
The general behavior is for the device to select Wi-Fi in preference to cellular whenever it is available. Whilst this is a simple decision, it can be inefficient as this behavior takes no account of the quality of connection available on each radio and also takes no account of the overall loading on each network.